Tandem quadrupole mass spectrometer

Abstract

All data obtained from an A/D converter during a summation period with values exceeding a prescribed threshold is excluded from summation up to a prescribed maximum number of deletions, and the values of the remaining data are summed to find one piece of measurement data corresponding to that summation period. The number of pieces of noise data reflecting the influx of particles that cause spike-like noise is extremely small, so noise data is removed in a state in which there are no signals and no target ions are present. When target ions are present, legitimate data which is not noise data may be removed, but the number of pieces of removed data is small in comparison to the total number of pieces of data, so the effects of the removal of legitimate data essentially do not emerge in the summation results. It is therefore possible to effectively reduce spike-like noise.

What is claimed is: 
     
       1. A tandem quadrupole mass spectrometer equipped with an ion source, a preliminary mass filter for selecting and transmitting ions having a specific mass-to-charge ratio from various ions produced by said ion source as precursor ions, a collision cell for splitting said precursor ions to produce product ions, a subsequent mass filter for selecting and transmitting ions having a prescribed mass-to-charge ratio among the produced product ions, and a detector for detecting the ions passing through said subsequent mass filter, wherein said tandem quadrupole mass spectrometer is provided with:
 a) an A/D conversion means for converting a signal obtained by said detector into digital data with a prescribed period; 
 b) a data value assessment means for assessing whether the value of digital data obtained by said A/D conversion means exceeds a prescribed threshold; and 
 c) a data summation means for finding measurement data of each summation period for all data obtained by said A/D conversion means during the summation period by excluding from summation the maximum predetermined number of pieces of data with values assessed to exceed the prescribed threshold by said data value assessment means and summing or averaging the values of the data that has not been excluded.